Every retaining wall situation is different but they all have one thing in common they all need a solid base. For an example this is our process for concrete retaining wall blocks. We usually start out by excavating a trench 2-3' wide and 12-24" deep depending on soil conditions. We will then compact the existing sub layer of soil, install landscape fabric to help with stability, and then we will start re-filling and compacting the trench with 12" + - of class 2 or 5 gravel, crushed concrete, or crushed rock whatever the conditions call for. We then level in a base course of block the is buried below grade for stability and then start stacking the material on top of that. We use any required drainage and reinforcement material including pea rock backfill, 4" perforated drain tile with outlets if necessary as well as geo-grid for stability. 

  To start the process I will come out to the site and look things over with the client and get any measurements I think I may need and take a couple pictures. I will then sit down with the client and go over any wants/needs/concerns about the project. I will then put together a proposal and perhaps a design if necessary and set up another meeting with the client to go over everything and make any adjustments if necessary. If the client is ready to commit to the project we can then go over payment options, lock down an approximate start date as well an approximate timeline for the project duration.  We usually ask for a deposit of 1/3 the projected amount to lock in a spot before ground is broken and the balance when the project is completed.